Multileaf lettuce

ABSTRACT

The invention relates to a new characteristic of lettuce which is referred to as multileaf characteristic and comprises the capacity to cause the formation in lettuce plants with a determined leaf morphology at the ready-to-harvest stage of significantly more leaves than in lettuce plants with the same leaf morphology which do not contain the characteristic. The term “significantly more” comprises: at least 1½ times as many as a lettuce type with a comparable leaf morphology, preferably at least twice as many, more preferably at least 2½ times as many, most preferably at least 200 leaves, at a ready-to-harvest stage and a determined head weight. The invention further provides a lettuce plant of the genus Lactuca in addition to a lettuce plant of the species  Valerianella locusta  L. (lamb&#39;s lettuce), both with the multileaf characteristic, seed of such lettuce plants and heads of lettuce.

The present invention relates to a new head form characteristic inlettuce, to use of the new characteristic in the development of newtypes of lettuce plant which differ morphologically from the lettuceplants known heretofore, and to heads of lettuce which contain thischaracteristic and thereby differ morphologically from known heads oflettuce.

A great diversity of lettuce varieties exists nowadays. At present morethan a thousand cultivars are known which can be divided roughly intothe groups butterhead lettuce, iceberg lettuce, batavia lettuce, coslettuce or romaine lettuce, oakleaf lettuce and lollo lettuce. Thisclassification is based on the morphology of the leaf and the degree ofhead forming. However, other classifications are used in addition tothis one. The UPOV list of descriptions of lettuce varieties thus refersfor instance to the following six groups: butterhead lettuce, crisplettuce, cos lettuce, “Grasse” lettuce, cutting lettuce and stemlettuce.

The known head lettuce, also known as butterhead lettuce, and theiceberg lettuce have the drawback that in these types of lettuce theouter leaves of a head of lettuce are clearly much larger than the innerleaves. For applications wherein cut or peeled whole leaves are used,such as in sandwiches, on hamburgers and the like, leaves of the mostuniform possible size are preferred. In the case of heads of lettucewith a clear heterogeneity in leaf size, such as the head-forminglettuce types butterhead lettuce or head lettuce, iceberg lettuce,batavia lettuce, cos lettuce or romaine lettuce, and “Grasse” lettuce,the outer large leaves will either be unusable or will always have to bereduced in size before use by means of cutting or tearing. Browningoccurs quite quickly on the cut or torn edges whereby the lettuce losesits attractive appearance and rotting can also occur more rapidly.Similar problems occur in automatic processing into cut lettuce.

It is the object of the invention to provide a new type of lettuce withwhich the above described problems can be avoided.

According to the invention a type of lettuce is now provided which, incomparison with the known types of lettuce, comprises significantly moreleaves of substantially equal dimensions at the ready-to-harvest stage.“Of substantially equal dimensions” is understood to mean that theleaves of this so-called multileaf type have on average a shorter lengthand lower weight relative to a normal lettuce plant with a comparableleaf morphology and comparable plant weight.

In the case of butterhead lettuce of the new type, due to thesignificantly higher number of leaves and the average shorter leaflength, a large number in absolute sense, and a large part in relativesense, of the harvestable leaves falls within the size of 4 to 12 cmleaf length (see Table 1).

Lamb's lettuce of the new type (Valerianella locusta L.) likewise hasmore leaves which have a smaller leaf size than lamb's lettuce plantsnot having the characteristic according to the invention (see Table 4).

“Significantly more leaves” is understood to mean in this case at least1½ times as many as a type with a comparable leaf morphology at equal(or comparable) plant weight, preferably at least twice as many, morepreferably at least 2½ times as many, most preferably at least 200leaves of substantially equal dimensions.

The lettuce provided according to the invention is per se a new type butcan have different leaf morphologies which in turn originate from othertypes of lettuce. The type of lettuce according to the invention ishowever always “multileaf” lettuce.

The characteristic “significantly more leaves of substantially equaldimensions” is a new head form characteristic and will be furtherdesignated “multileaf” characteristic and likewise form part of theinvention. The presence of the multileaf characteristic in a lettuceplant can be determined simply by comparing the total number of leavesof a ready-to-harvest lettuce plant suspected of possessing themultileaf characteristic with the total number of leaves of aready-to-harvest lettuce plant which is comparable in respect of leafmorphology and plant weight but which certainly does not possess themultileaf characteristic (control plant). When the suspected multileaflettuce plant has at least 1½ times as many leaves as the control plant,it can be stated that the multileaf characteristic is present. In suchplants use is in that case made of the characteristic according to theinvention. Use has also been made of the characteristic in themanufacture of such plants. These types of use also form part of theinvention.

The multileaf characteristic means in fact that plants have a geneticconstitution which enhances the occurrence of fasciation at a determinedstage of the vegetative growth. Fasciation in butterhead lettuce occursat a relatively early stage of the vegetative growth, while in lamb'slettuce the characteristic is expressed only at a later stage of growth.

Fasciation, also referred to as band formation, is a per se undesiredphenomenon which can occur in many types of vascular plants. It wasalready described in 1948 by White in “Fasciation”, Bot. Rev. 14,319-358 (1948). Fasciation in lettuce is characterized by the apex of astem becoming increasingly wide when it begins to lengthen. Acone-shaped apex normally results. In the case of fasciation however, aflat, wide and comb-like (grooved) band of meristematic tissue isformed. It is known that fasciation in lettuce has a genetic basis andis inherited recessively (Haque & Godward, Genetica-Iberica 38, 139-155(1986)) or additively (Eenink & Garretsen, Euphytica 29, 653-660(1980)). In addition, influences of environmental conditions on theexpression of fasciation have also been described (Eenink & Garretsen,supra).

Fasciation in lettuce is a phenomenon which has been known for some timeand which was long considered mainly as disadvantageous, because linessubmitted for registration under the UPOV Treaty often did not reactuniformly to fasciation and because fasciation hinders seed production.Fasciation does however also have a positive side, since fasciatedplants are slow-bolting, which is a particular advantage for greenhousevarieties in the summer period.

According to the invention the phenomenon of fasciation has now beenused to arrive at an entirely new type of lettuce. By specific selectionit has been possible to increase, respectively advance the degree andthe time of fasciation, whereby a fasciated apex is already formed, forinstance in butterhead lettuce, at a very early stage of the vegetativegrowth. The final lettuce plant hereby acquires a rosette-like headwhich is built up of a very large number of leaves of substantiallyequal size on a greatly enlarged stem base.

In lamb's lettuce the characteristic occurs later, but at theharvestable stage the differences from lamb's lettuce plants notdisplaying the characteristic is very clearly visible.

The advantage of the new lettuce plants according to the invention isthat a very large number of leaves of substantially equal dimensions canbe cut from one head of lettuce. Moreover, owing to the greatlyincreased circumference of the stem, the leaves can be cut from the stemat the location of their petiole more easily than in lettuce types witha comparable leaf morphology. Only a limited cut surface hereby resultsand the leaves them-selves remain intact.

Owing to their substantially equal dimensions, the leaves areparticularly suitable for use on for instance sandwiches or hamburgers,or in pre-cut salads.

In lamb's lettuce the multileaf characteristic results in a differentmanner of growth. In lamb's lettuce not displaying the multileafcharacteristic (further referred to as “normal” lamb's lettuce) theleaves are crossed in pairs. In the multileaf lamb's lettuce the leavesare placed in groups as rosettes. The head consists of large numbers ofsuch rosettes.

Described and shown in the accompanying examples and figures asillustration of the invention are the obtaining (example 1), the degreeof expression and inheritance (example 2) and the appearance (figures)of a head of lettuce with a leaf morphology of butterhead lettuce.Example 3 shows the differences between “normal” lamb's lettuce andlamb's lettuce according to the invention.

The multileaf characteristic can however also be combined withcharacteristics of other types of lettuce, such as leaf shape, leafthickness, serration, leaf colour and leaf consistency (for instancecrispiness). These characteristics can be transferred from other lettucetypes to the type described herein. This transfer can take place bymeans of recombinant DNA techniques and/or by conventional crossing-in.The variants which result in this manner likewise fall within the scopeof the present invention.

“Leaf morphology” is understood to mean the whole of the phenotypicalcharacteristics which provide a leaf with the appearance characteristicof the associated lettuce type.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 show respectively the top, bottom and cross-section of a headof multileaf butterhead lettuce according to the invention. By way ofcomparison, FIGS. 4 and 5 show top and bottom views of a head ofbutterhead lettuce. On the underside of the head of multileaf lettuce isclearly visible that the head possesses a larger number of leaves ofsmaller dimensions than the head of butterhead lettuce. FIG. 6 shows atypical head of multileaf lettuce from which the stem base has beenremoved. FIG. 7 shows a comparison between the removed leaves of a headof butterhead lettuce (top) and a head of multileaf butterhead lettuceaccording to the invention (below).

The present invention will be illustrated with reference to theaccompanying examples.

EXAMPLE 1

Obtaining Butterhead Lettuce Plants with Multileaf Characteristic

A hybridization was made (designated with the number 5358) between twolettuce plants of the butterhead lettuce type. This was a hybridizationbetween two selection lines of applicant. The mother had code 16487 andthe father had F4[1366 OPG×F2 (15336×Troppo×1600×Bizet)].

In the F2 of this hybridization a plant was found a year later withfeatures such as the plant of the invention. Seed was recovered fromthis plant and this seed was sown the following year in order to assessthe external features on a larger number of progeny plants. Of —these F3plants a number of plants were selected once again on the basis of thecombination of (new) phenotype according to the invention and otherquality-determining features (leaf thickness, leaf shape, leaf colour,head shape, head structure, yield, resistance to downy mildew, etc.).

This process of line selection was continued in the following 10 years,and a pure line was thus obtained (designated with the number 5338).This line is a good combination of a new phenotype according to theinvention and the other quality-determining features.

For a further improvement of the phenotype of the plants of theinvention, this line was crossed two years later with the variety S0256.In the progeny of this hybridization a rigorous selection was once againmade from the F2 for plants with a very large number of leaves ofsubstantially equal dimensions, combined with attractive leaf and headfeatures and other features desirable for the culture of lettuce. Afterplant selection in the F2 and line selection from the F3 generation, asufficiently pure line was finally obtained three years later, which isdesignated with the number RZ 97.41561, and seed of which was depositedon 1 April 1997 at The National Collections of Industrial and MarineBacteria Limited (23 St. Machar Drive, Aberdeen AB2 1RY, Scotland, UK)under number NCIMB 40877 in order to illustrate the invention.

EXAMPLE 2

Decree of Expression and Inheritance of the Multileaf Characteristic

Plants of several standard varieties of the butterhead lettuce type forgreenhouse culture (Floris RZ, Vegas RZ and Limit RZ), of two multileaflines (No 5338 and RZ 97.41561) and of an F2 between a normal butterheadlettuce line and the multileaf line No 5338 were sown and furthercultivated. The cultivation took place under a standard cultivationregime for greenhouse lettuce. The observations are an average of 4plants per variety or line. The plants were prepared as for auctionbefore assessment, i.e. old leaves with deposits or yellowed leaves wereremoved.

TABLE 1 Average head weight in grams (± SE), number of leaves (N) with aleaf length greater than 4 cm distributed over a number of lengthclasses (± SE), and the quotient of the average head weight and thetotal number of leaves longer than 4 cm (± SE) of three butterheadlettuce varieties (not multileaf) and two multileaf lines MultileafWEIGHT % in size Variety/line ? (grams) N 4-8 cm N 8-12 cm N 12-16 cmN > 16 cm Ntotal (>4 cm) 4-12 cm WEIGHT/Ntotal Floris RZ no 383 + 33 7.89.8 16.5 0.0 34.0 ± 3.1 52 11.3 ± 0.33  Vegas RZ no 464 ± 80 8.8 8.521.5 5.0 43.7 ± 4.6 40 10.6 ± 0.94  Limit RZ no 410 ± 34 19.8 10.5 23.35.8 59.2 ± 5.6 51 6.9 ± 0.84 No 5338 yes 419 ± 39 44.8 43.5 50.5 0.0138.8 ± 25.3 68 3.0 ± 0.25 RZ 97.41561 yes 430 ± 29 168.0 87.8 19.5 0.0275.3 ± 35.2 93 1.6 ± 0.18

Table 1 illustrates the differences which can be found in commercial(non-multileaf) butter lettuce varieties for the number of leaves longerthan 4 cm: Floris RZ has relatively few leaves, the variety Limit RZ hasalmost twice as many in the category longer than 4 cm. The variety LimitRZ was included in this experiment because it was known that thisvariety forms relatively many leaves. However, the multileaf line No5338 has more than twice as many leaves in the measured category thanLimit RZ, and the line RZ 97.41561 even has four times as many. Thisincrease in the number of leaves is accompanied by a sharp increase(both absolutely and in percentage terms) of leaves in the lengthcategory of 4-12 cm and a sharp decrease in the average weight per leaf.

76 plants of the F2 (butterhead lettuce×No 5338) were assessed. Thebutterhead lettuce which was used for crossing closely resembled VegasRZ in respect of morphology. Table 2 gives the frequency distributionfor the number of leaves longer than 4 cm per head of lettuce. Table 3shows the frequency distribution for the quotient of the head weight andthe number of leaves longer than 4 cm.

TABLE 2 Frequency distribution for the number of leaves longer than 4 cmof 76 plants of an F2 population from a hybridization between abutterhead lettuce line (not multileaf) and No 5338 (multileaf). Class:number of leaves longer Number of than 4 cm plants <40 0 40-50 7 50-6024 60-70 20 70-80 6 80-90 2  90-100 5 100-110 1 110-120 2 120-130 2130-140 1 140-150 2 150-160 2 160-170 1 >170 1 >Total 76

TABLE 3 Frequency distribution of the quotient of the head weight andthe number of leaves longer than 4 cm of 76 plants of an F2 populationfrom a hybridization be- tween a butterhead lettuce line (not multileaf)and No 5338 (multileaf). Class: Head weight/Number of leaves > Number of4 cm plants <3.0 0 3.0-3.5 8 3.5-4.0 2 4.0-4.5 5 4.5-5.0 2 5.0-5.5 25.5-6.0 2 6.0-6.5 0 6.5-7.0 1 7.0-7.5 5 7.5-8.0 11 8.0-8.5 16 8.5-9.0 129.0-9.5 8  9.5-10.0 2 >10 0 Total 76

Table 2 shows that the number of leaves larger than 4 cm per plant has acontinuous distribution with a peak at 50-60 leaves larger than 4 cm perplant and with 17 plants having more than 90 leaves larger than 4 cm.These latter 17 plants were all of the multileaf type. The fact that nodiscontinuous segregation of the multileaf characteristic was obtainedmay be because the plants differed mutually in plant size and weight.The average head weight of the F2 plants varied from 350 to 655 g. Incontrast to the number of leaves per plant, the quotient of head weightand number of leaves does give a discontinuous distribution, with 21plants having a quotient smaller than 6.0 (all of the multileaf type)and 55 plants having a quotient greater than 6.5 (all of the normaltype). The segregation corresponds with a monogenic recessiveinheritance of the multileaf characteristic.

Within the group of plants of the multileaf type a further segregationwas found, which indicates that the degree to which a plant has themultileaf characteristic is also determined by other genes. This is alsosupported by the fact that it was possible, starting from line No 5338(an average of 139 leaves longer than 4 cm, see Table 1), to obtain aline via hybridization and specific selection having an average of 275leaves longer than 4 cm (RZ 97.41561, see Table 1).

EXAMPLE 3

Obtaining Lamb's Lettuce Plants with Multileaf Characteristic

In the same manner as described in Example 1 a hybridization was madebetween two lettuce plants of the lamb's lettuce type. The selection ofplants according to the invention and further obtaining of a pure linecan likewise be realized in similar manner.

Seed of this line, which is designated with the number RZ 98.44080, wasdeposited on Jul. 15, 1998 at The National Collections of Industrial andMarine Bacteria Limited (23 St. Machar Drive, Aberdeen AB2 1RY,Scotland, UK) under number NCIMB 40960 in order to illustrate theinvention.

It was found from hybridizations of the plants according to theinvention with “normal” lamb's lettuce plants and selection of linesthat the multileaf characteristic is inherited recessively and isgenetically stable. The characteristic is expressed only at a laterstage of the growth. In the initial stage of growth there are nodifferences between the type according to the invention and “normal”lamb's lettuce. The final leaf size is found to be smaller in the typeaccording to the invention than in the “normal” type. The size of plantsaccording to the invention is however comparable to “normal” lamb'slettuce plants. It was found from counts (see also Table 4) that 30 to70 leaves are formed in “normal” plants, while this number variesbetween 130 and 210 leaves in plants according to the invention.

TABLE 4 Number of leaves per type lamb's lettuce plant “normal” lamb'snumber of according to the Number of lettuce plant leaves inventionleaves 1 50 1 160 2 27 2 154 3 33 3 188 4 37 4 204 5 50 5 172 6 61 6 1607 37 7 210 8 42 8 160 9 70 9 170 10  42 10  130

What is claimed is:
 1. A lettuce seed designated RZ 97.41561 havingNCIMB number
 40877. 2. A lettuce plant or its parts produced by the seedof claim
 1. 3. The plant of claim 2 wherein the plant has a multileaftrait.
 4. A lettuce plant having all the morphological and physiologicalcharacteristics of the plant of claim
 2. 5. A lettuce seed produced fromthe plant of claim
 2. 6. A method for producing first generation hybridlettuce seed comprising crossing a first parent lettuce plant with asecond parent lettuce plant, wherein said first or second parent lettuceplant is the plant designated RZ 97.41561 having NCIMB number 40877, toproduce first generation lettuce seed.
 7. Seed produced by the method ofclaim 6.